Tune Out the Pandora Rally

The Internet radio service's stock soared as quarterly results cheered investors. However, rising costs and stiff competition may pressure shares.

Pandora opened its quarterly financial box late Thursday and out poured enough positive numbers to send the Internet radio service's stock soaring.

But with shares of Pandora Media (ticker: P) up 17%, or $2.04, to $13.77, in Friday afternoon trading, investors would do well to look elsewhere. With more than 60% of the company's shares sold short as of mid-February, many were likely scrambling to cover their bearish bets today.